Ligand Exchange Reactions and Hydroamination with Tris(oxazolinyl)borato Yttrium Compounds

Ligand substitution reactions and catalytic hydroamination/cyclization of aminoalkenes have been studied with a new oxazolinylborato yttrium compound, tris(4,4-dimethyl-2-oxazolinyl)phenylborato bis(trimethylsilylmethyl)yttrium ([Y(κ3-ToM)(CH2SiMe3)2(THF)], 1). THF exchange in 1 is rapid at room temperature, and activation parameters obtained by simulation of 1H NMR spectra acquired from 190 to 280 K are consistent with a dissociative mechanism (ΔS‡ = 30 ± 1 e.u., ΔG‡ = 11.9 kcal mol−1 at 243 K). The related phosphine oxide adduct [Y(κ3-ToM)(CH2SiMe3)2(OPPh3)] (2) also undergoes exchange via OPPh3 dissociation with a much higher barrier (ΔG‡ = 15.0 kcal mol−1 at 320 K). Compound 1 reacts with the amines tBuNH2, para-MeC6H4NH2, and 2,6-iPr2C6H3NH2 to provide six-coordinate [Y(κ3-ToM)(NHR)2(THF)] (3: R = tBu; 4: R = para-MeC6H4) and five-coordinate [Y(κ3-ToM)(NH-2,6-iPr2C6H3)2] (6). These oxazolinylborato yttrium compounds are precatalysts for the cyclization of aminoalkenes; the kinetics of catalytic conversion indicate zero-order substrate dependence and first-order catalyst dependence. Kinetic investigations of ligand exchange processes and hydroamination reactions indicate that the tris(oxazolinyl)borato-yttrium interaction is robust even in the presence of excess phosphine oxide and primary and secondary amines

Somatostatin and its analog enhance the formation of human leukocyte migration inhibiting factor: Further evidence for immunomodulatory action of somatostatin

The effect of somatostatin-14 (SST) and somatostatin analog D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-NH 2 (RC-102) on migration inhibition of human leukocytes induced by cardiac antigen or phytohemagglutinin (PHA) was investigated. Both SST and RC-102 augmented the migration inhibition, thus indicating the enhanced formation or action of the leukocyte migration inhibiting factor (LMIF). This finding provides additional evidence for the immunomodulatory action of somatostatin